In recent years, as there is an increasing amount of data to be processed in a company, a storage apparatus comes to include a large number of memory devices, and the memory device increases in capacity year by year. In general, an HDD (Hard Disk Drive) is installed as a memory device; however, in place of the HDD, in recent years, attention is focused on a memory device (an SSD: Solid State Device, for example) having, as a memory medium, a non-volatile semiconductor memory (a flash memory, for example). Although the SSD is more expensive than the HDD, the SSD performs I/O process at an extremely high speed.
In the flash memory, a physical storage area is managed by a unit referred to as a “block”, and the data is erased by such block. There is an upper limit on the number of times that the block is erased, and when the number of times of erasure increases, it may be difficult to write data into the flash memory or it is likely that an error occurrence rate of data written into the flash memory increases. That is, the flash memory has a life-span, and the SSD having a large number of flash memories also has a life-span. As refinement of a flash memory chip is developed, the flash memory chip comes to possess a large capacity, and on the other hand, reliability is decreased and there occurs an issue that die-by-die or chip-by-chip quality is not consistent, for example. The die of poor quality tends to increase an error occurrence rate and becomes unusable due to a failure even when the number of times of erasure is less than a predetermined number. When such a failure occurs in a plurality of dies, it is not possible to ensure a storage area which stores user data and there is no choice but to close the memory device. Thus, when an SSD becomes unusable at an earlier stage than a predetermined period, a replacement frequency may increase and a cost for purchase and maintenance of an SSD may occur.
For example, PTL 1 discloses a data recovery technology performed when a failure occurs in a block in an SSD. There is known a technology in which when, in a storage apparatus having a plurality of SSDs, a failure of a block in a certain SSD is detected, all data, including a failed block, in the SSD are rebuilt in a different SSD.